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Teachers’ notes | Atmosphere, weather and climate

2.1 Key factors behind Antarctica’s climate

The first question requires students to consolidate their knowledge of Antarctica’s general climatic conditions, both from the text and from any of the suggested weblinks. As a factfile, students could use separate headings (or create a table with columns for each variable) to summarise temperature, precipitation, etc. There should be some reference to averages and ranges, and the climate factors involved. As an essay, the answer should be more discursive, with a greater emphasis on explanation. Explanation should include reference to the concepts of ‘angle of incidence’ (controlled by latitude), ‘albedo’, ‘continentality’, and ‘elevation’.

Question 2 challenges the common misconception that the coldest place is the South Pole. Answers should refer to the fact that the coldest temperature ever recorded was at the Vostok Station (East Antarctica): a key reason is the difference in elevation between the two stations.

Question 3 requires students to do a little extra research on the Arctic so that they can compare and contrast the two polar regions by drawing upon some actual facts and figures. The suggested websites (particularly the nsidc website, and the new ‘Discovering the Arctic’ website provide information on the climate of the Arctic. Students will find that the Antarctic is considerably colder and drier than the Arctic: temperatures on the East Antarctic Ice Sheet routinely fall below -50°C; whereas temperatures near the North Pole rarely fall below -30°C. (The coldest Northern Hemisphere temperature was recorded in north-east Siberia, not at the North Pole.) Some of the same climate factors are at work (e.g. angle of incidence and albedo); but the key differences are caused by the differing geography of the two regions in terms of the distribution of land and sea, as well as the different average elevations.

Question 4: after students have been through the material in Section 2.1, the quiz at the Antarctic Connection website is a good way for students to test and review their knowledge.

2.2 Regional climate variation and weather

Question 1 is intended to familiarise students with the various Antarctic research stations where weather and climate data are recorded. The data from the various stations listed are important for characterising differences in weather and climate across the continent. By using the ‘gisdata’ website (provided by the USGS) to locate the stations, students will gain some experience of a ‘GIS-style’ resource. In addition to finding the stations, students should be encouraged to experiment with the search functions of the programme so that they can see how different ‘layers’ of geographical information can be displayed or hidden on the base map.

Question 2 is a skills question asking students to manipulate, graph, and interpret climate data from a selection of Antarctic stations. Graphs can be drawn on Excel or by hand, and should be organised so that each month is a category along the X-axis and the variables of mean monthly temperature, precipitation (where available), and windspeed (where available) are plotted with respect to the Y-axis. After graphs have been drawn (and mean annual statistics calculated), question 2b requires that students describe the climate in brief for each of their chosen stations. Question 2c asks students to explain the factors causing Vostok to have the lowest mean annual temperature – a key cause is its high elevation. Question 2d asks students to explain the factors causing Mawson to have the highest average windspeed – this should involve a discussion of Mawson’s topographic position near the edge of the sloping East Antarctic Ice Sheet and the phenomenon of katabatic winds.

Question 3 is evaluative: students should be able to apply their understanding from both Sections 1.1 and 1.2 to give a reasoned account for the differences in climate across the continent. Strong essays will refer to a range of different climate variables and will use facts and figures (and reference to actual stations) to illustrate how different factors (latitude, altitude, etc.) alter the climate across the continent.

2.3 Climate change: past and future

Question 1 revises the nature of the evidence contained in ice cores and the importance of ice cores for climate studies. Students can rely on the text for much of their write-up; but should be encouraged to follow up a few of the suggested weblinks (especially the links) to widen their knowledge. Important points are that ice cores are one of the best forms of ‘palaeoclimatic archives’ in that they can tell us many different things about how the atmosphere has changed through time, and they can be dated to a higher degree of precision and accuracy than many other forms of evidence (such as sediments on the sea bed or on land). Crucially, they give us a long-term perspective on natural changes against which recent human effects can be measured and assessed.

Question 2 is a data response-style question, asking students to unpick the temperature and carbon dioxide data from the EPICA ice core. Students should have a copy of the graph in front of them when attempting to answer the list of questions. In order the answers are: 8 glacial/interglacial cycles are fully represented in the ice core data; the frequency is roughly 1 cycle every 100 000 years; the warmings appear to have occurred more rapidly than the coolings (creating a ‘saw tooth’ pattern to the graphed data); there are only four previous times in the record when temperatures were approximately as warm as today (roughly 400 000, 325 000, 225 000, and 120 000 years ago); we would expect a cooling trend over the next several thousand years in the absence of human modification of the climate; there is a close relationship between temperature and carbon dioxide over the time spanned by the diagram (similar timing of peaks and troughs); today carbon dioxide is about 30% higher than what is normal for a warm, interglacial phase; even though climate warming begins slightly before the increase in carbon dioxide, most climate scientists believe that as carbon dioxide rises it causes further warming to occur through ‘positive feedback’ – hence the ice cores offer good evidence that carbon dioxide is an active contributor to climate warming. The greenhouse gas feedback apparent in the ice core data may also be involved in causing the warmings to be more rapid than the coolings shown in the record.

Question 3a is a skills question requiring students to use Excel to process and graph instrumental climate data in two forms – as a time series and as a correlation scatter plot. The time series shows a trend of increasing temperature from 1945 to 2008 (superimposed on year-to-year variability). The trendline indicates that temperatures have risen on average from about -5.5°C to -2.5°C over the time period shown (a rise of 3°C over 63 years, or a rate of approximately 0.05°C per year). The second graph should show a weak positive correlation between carbon dioxide content of the atmosphere (as measured at Mauna Loa, Hawaii) and mean annual temperature at Vernadsky. (Students may need to spend more time manipulating this graph to get the right scales and appearance: e.g. the X-axis should cross at -9°C). The trendline shows an increase of temperature of approximately 0.04 for every 1ppm increase of CO2; however, the relationship is not a strong one: many points are far from the trendline, and the R2 value of about 0.3 indicates that only about 30% of the variation in temperature is explained by variation in CO2.

Question 3b asks students to interpret the correlation plot that they have drawn. A circumspect answer would be that the plot is consistent with the hypothesis that increasing carbon dioxide should cause warming; but correlation does not necessarily equal causation, and there are clearly other factors influencing the temperature at Vernadsky given the weakness of the correlation. One should be careful in drawing conclusions from a single site because of the possible effects of local factors and random variations. Additional evidence could come from analysing similar correlations based on data from other areas around the Peninsula and the continent as a whole. A statistical test of correlation could be conducted on the data graphed to test whether or not the relationship is significant (i.e. is unlikely to have occurred by chance). Continued monitoring is also important, as firmer conclusions can be drawn from larger data sets.

Question 3c probes students’ understanding of the nature of correlations, and ‘dependent’ and ‘independent’ variables. The choice of plotting CO2 on the X-axis in this case is justified because local temperature will have a negligible effect on globally averaged values of CO2 concentration. If globally averaged temperatures were used, the justification would be less secure because at the global scale there is a two-way relationship between CO2 and temperature. E.g. warmer global temperatures can lead to increases in atmospheric carbon dioxide because warm water cannot dissolve as much CO2 and because in a warmer climate, carbon is more rapidly released through plant decomposition. Because the carbon cycle is influenced by temperature at the global scale, in the second case, CO2 variation cannot be considered independent of temperature.

2.4 The ozone hole

Question 1 requires students to review and consolidate their knowledge of the ozone hole problem from the concepts introduced in the text. They should also be encouraged to explore some of the weblinks suggested in the resource. The write-ups should address the aspects of the problem listed in the bullet points; the key ideas being: that the ozone hole is a depletion of the ozone layer in the stratosphere within the south polar region, that the photochemical reactions involved are enhanced by certain atmospheric conditions prevailing in the austral spring, that these conditions are more intense in the Southern Hemisphere than in the north, that the Montreal Protocol was set up to address the problem, and that the problem (while being solved) continues due to the long residence time of ozone depleting chemicals in the atmosphere.

Question 2 is another skills question requiring students to process, graph and interpret data in an Excel spreadsheet. For Question 2a, students need to draw two time series graphs (one showing changes in October ozone concentration over time and another showing changes in annual CFC-11 emissions over time) and one correlation scatter graph (comparing CFC-11 emissions and October ozone). The first graph shows that October ozone has declined dramatically over the period of record, especially during the 1970s and 1980s. The range between the highest and lowest ozone readings is 201 Dobson units, and this represents an ozone decline of roughly two thirds of normal values due to human activities. The second graph shows a steep rise in CFC-11 during the 1960s and 1970s. There is a dip centred around 1980, with another peak in CFC-11 release in the late 1980s. The Montreal Protocol came into force in 1989 (this date should be annotated on the graph), and since then CFC-11 release has been in decline. The third graph shows a negative relationship between CFC-11 release and ozone concentration (CFC-11 is the independent variable and should be on the X-axis.) The trendline is fairly steep showing a large decline in ozone as CFC-11 increases; although the correlation, while significant, is not very strong (R2 value of approximately 0.5).

Questions 2b, 2c, and 2d are data response-style questions based on the graphs. For 2b, the third graph shows the relationship expected between the two variables (that CFC-11 reduces stratospheric ozone); although there is a good deal of year-to-year variation in ozone shown in the graph that is not explained by the CFC-11 values. For 2c, the anomalies can be explained by the fact that CFC-11 isn’t the only ozone depleting chemical and that other factors are also involved, particularly year-to-year variations in the weather in the stratosphere – such as the amount of stratospheric clouds which play a key role in ozone destruction. The answer to 2d requires students to remember from the text that ozone depleting chemicals tend to have a long ‘residence time’ in the atmosphere. This is why the first graph shows low October ozone values in recent years despite the reduction in the emission of these chemicals.

Question 3 is an evaluative question that lends itself to an essay-style answer. It should only be attempted by students who have gone through both Sections 2.3 and 2.4 since it demands a comparison between the two different problems. There is plenty of scope for students to go into detail about the causes and consequences of the two problems; but at the heart of the essay should be a recognition of the different scales of the problems and solutions. The cause of ozone depletion was found to be quite straightforward and there was little debate about the existence of the problem and what needed to be done to tackle it. This made the Montreal Protocol relatively easy to achieve. In contrast, there has been much debate about the causes and potential impacts of recent climate warming, and significant disagreements remain between countries about how to deal with the problem. Unlike reducing ozone depleting chemicals, reducing greenhouse gas emissions also requires big (and in some cases difficult) changes in how we produce and use energy, and ultimately in our lifestyles.